I'm having serious smoke problems coming out of the exhaust on my JD L120 riding mower. Constant white smoke that gets worse under load with much knocking and pinging, black smoke at severe loads. I'm considering working on the engine myself as a learning project as I have all the manuals which very clearly explain how to tear the engine down, check the boring, rebore if necessary, replace the rings, etc. It would be a hobby project to get myself some mechanical skills as I had fun rebuilding the carb (although the black smoke indicates I probably need to do some adjustment).

Trouble is, I need the mower this season and am willing to purchase a new engine for it but I'm having a hard time figuring out which engines I can use as replacements. I found a great deal on a 25hp Intek that looks exactly like my 20hp Intek and there are numerous new engines on eBay.

How can I determine with certainty if a particular engine will drop into my L120 chasis? I believe my engine is a 407777 0131YC (from memory so may not be exact), but how can I use the Model and Type information to look for replacement engines that will fit?

I would look at the possibilities of other issues on your engine that may be worth fixing. Lawn equipment especially cast iron bore units very rarely wear out unless EXTREMELY high usage and or a poor air filtration unit.

What you are describing is a classic B&S over oil or fuel seeping into crankcase issue. Check and change the oil, look and smell to see if it has fuel in it and make sure the breather hose from crankcase to airfilter is not pinched or plugged.

If you do have fuel in crankcase replace carb, money better spent.

If you want the replace the engine the spec# will help but you will need to look up crank diameter and the location of controls. Other than this the engines have the same bolt pattern and will adapt.

Don

Thanks for the quick response, Don! Obviously, I'd much rather fix this engine then buy a new one, but I don't want to be down for more than a couple of weeks.

I have not over oiled the engine and just changed the oil. After mowing the oil level is down by HALF so there is a lot of oil coming out of the exhaust. I believe the black smoke indicates fuel in the crankcase and that is only under extreme load.

Trouble is, I *just* rebuilt this carburetor. Granted, I could have done something incorrectly but I got to say it *sure was easy* to rebuild and I cannot imagine where I went wrong. It is certainly not a complicated procedure. I did not do the RPM adjustments as explained in the engine manual, so I suppose I'll give that a whirl. I also did not use the "LocTight" stuff as I could not find it locally and was in a hurry to mow before the neighbors showed up with pitchforks and machetes. Could that be the problem?

I'll make sure the breather tube is not clogged as well, as you suggest.

Also, the reason I rebuilt the carb in the first place was because I ran this mower the better part of last season in a dusty, dirty environment without the air cleaner cover on properly. The inside of the air horn and air cleaner intake where covered with dirt and grime so I figured it couldn't hurt to clean up the carb. Turns out the carb was actually very clean and I could have re-used all the gaskets (although I replaced them anyway).

Could an incorrectly seated air cleaner cover be the cause of my engine problems? I replaced the spark plugs which were also covered in carbon deposits and am considering taking the cylinder heads off and cleaning up the tops of the cylinders.

Assuming the carb and the breather tube are working properly, how would I fix this classic problem? I'll check the oil for fuel and mess with the carb some more, but it sure seems like rings to me (not knowing any better).

Thank you again!

You hit the nail on the head, the only way to get extreme wear on that unit would be bad air filtration, Does the throttle shaft move back and forth (side to side) in the carb? If so that is a sign of the wear the cylinder and piston were subject to.

I would look to either replacement or repair at this point.

Tough luck
Don

Actually, the throttle shaft and the rest of the entire carb are all very clean and not worn at all. The throttle shaft was just fine and does not move back and forth once it's slid into place.

It sounds like you're validating my suspicions and I should find a replacement engine. Then I'll take the old engine and play with it, learn how to bore it out and install oversized pistons and all that sort of thing. I might even sell it to someone on eBay if it turns out well. I do appreciate your responses and helping me work through this!

So then, back to my original question:
I can use the Model and Type to determine which replacement engine I can use, but I cannot find any description of what the digits of the Type represent other than "identifies certain unique features such as the crankshaft or governor spring used on an engine."

My engine is a 406777 0139 E1

It's helpful to know that the engine mounts will be mostly universal (assuming the engine looks similar), but what Model and Types should I limit my searches to?

I assume the displacement doesn't matter much (within reason), but do I need to limit to a particular design series? Most replacement engines I'm finding are all xxx777's.

Is there a reference to what the digits in the B&S Type code represent? Also, out of all my research and manuals, I can't for the life of me find the diameter and length of my current crankshaft.

I've found a great deal on a 445777 0231CO and I wonder if it would work with my L120 chassis. If that particular model would work, I'll just grab it and be done with my search.

I am more familiar with Honda's process, you can go to their web site and get schematics. Check briggs. The throttle shaft was a brain fart, that is a wear item as the engine wears under normal conditions and would not show accelerated wear in your situation. Maybe a briggs guy can answer your question better.

Don

Thanks again for your help. I just bought the new engine after speaking with Briggs tech support. Officially, the replacement engine is the same model, but unofficially any of the models should work assuming the same drive shaft length and width. The exhaust system is the same for all of these Briggs models. I got a great deal on that 25hp engine and will be installing it over the next couple of weeks, hopefully before it's time to mow again.

I'll update this thread when I'm done, for other's future reference.